[d33]

This inspired me to do this experiment:

dd if=/dev/zero bs=1K count=$(( 256 * 3 )) of=a.ext4

mfks.ext4 a.ext4

mkdir a

sudo mount a.ext4 a

cd a

sudo chown 1000:1000 .

python3 -c 'open("a", "wb").write(b"\xff\x00\x00" * 2000)'

python3 -c 'open("b", "wb").write(b"\xff\xff\x00" * 2000)'

python3 -c 'open("c", "wb").write(b"\xff\x00\xff" * 2000)'

cd ..

sudo umount a

(echo -n 'P6\n512 512\n255\n' ; cat a.ext4 ) > a.ppm

convert a.ppm a.png

The resulting a.png is reversible - you can convert it back to .ppm file, skip first 15 bytes and you should get a valid .ext4 back.

[pizzafeelsright]

if twitter didn't do compression it would be fun to store large files as images with twitter as a filesystem

[tecleandor]

Well, you can maybe put some qr codes less sensible to compression XD. OK, OK, it was a joke, just do some steganography.